Yeast Assimilable Nitrogen (YAN) Measurement in Wine
What is YAN?
- Nitrogens are present in grapes at amounts between 60 to 2400 mg N/L and include a wide variety of molecules: aminoacids, ammonium, peptide and polypeptide proteins, as well as smaller amounts of amines, amides, urea, pyrimidines, purines, nitrates and nitrites
- However, yeasts can only assimilate part of these compounds and make them part of their cell mass. This set of compounds is commonly known as yeast assimilable nitrogen (YAN)
- The compounds that comprise YAN are the ammonium ion (NH4 +) and primary amine nitrogen (PAN) provided by the aminoacids
Where Does YAN Come From?
- These nitrogen compounds came from the vineyard
Therefore, the winegrowing practices have a direct impact in their levels into the grapes. Low YAN is associated with low soil organic content and overall dry growing conditions - Nitrogen compounds present in must and wine play a major role in yeast fermentation so, must be controlled
- Early detection of nitrogen deficiency in grapes and juice can enable winemakers to make informed decisions regarding nitrogen additions using inorganic nitrogen (DAP) or organic nitrogen (proprietary yeast supplements)
Why YAN is Important?
- A minimum concentration of YAN (150 mg N/L) is needed for a correct fermentation
- Higher initial juice/must YAN values increase fermentation rate and heat production. DAP (diammonium phosphate) can be added in divided doses to give a more moderate rate of fermentation
- Nitrogen supplements can reduce the risk of slow or stuck fermentations. It also avoids the development of undesirable sensory characters such as hydrogen sulfide and reductive character
- YAN concentrations (250-350 mg N/L) are required to make more clean/fruity flavoured wines
- Big amounts of initial YAN or non-controlled DAP additions can increase the risk of residual YAN in finished wines. Excessive inorganic nitrogen can increase the risk of ester taint (ethyl acetate) formation
OIV Methods
The OIV International Compendium of International Methods of Wine and Must Analysis (2021 edition) describes three methods to determine nitrogen compounds:
- Total nitrogen (OIV-MA-AS323-02A: R2009)
- Total nitrogen (OIV-MA-AS323-02B: R2009)
- Ammonium (OIV-MA-AS322-01: R2009)
All three methods are manual and require significant amounts of time and human resources. However, OIV has no official method for the determination of YAN.
Usual Methods
YAN Determination by Titration Method:
- Formaldehyde Titration (Sorensen method): addition of a formaldehyde (a toxic liquid) solution and a valoration with sodium hydroxide
YAN Determination by Spectrophotometric Methods:
Ammonium can be measured using the enzyme known as glutamate dehydrogenase (GLDH)
Primary amine nitrogen can be measured using o-phthaldialdehyde (OPA) dye.
The sum of both components, expressed as mg N/L, indicates the YAN concentration.
Comparison of Methods
The methods were compared in order to evaluate the differences between formaldehyde titration (Sorensen method) and the BioSystems spectrophotometric methods for ammonium and PAN.
First Experiment
A total of 61 samples of cava-based wine were analyzed by stopping fermentation with NaF and taking parallel measurements.
The results indicate that there is a proportional difference of 7%.
Second Experiment
Further experiments based on aminoacids and ammonia quantification were performed to compare the methods.
The Sorensen method gives accurate results for ammonium but underestimates the primary amino nitrogen level by 20%. The spectrophotometric method responds properly to the expected ammonium and PAN concentrations at various concentrations and using two different aminoacids (aspartic acid and isoleucine).
Conclusions
The methods are equivalent, which means laboratories have two different tools to evaluate nitrogen nutrients present in the sample and necessary for fermentation. However, there are differences in how the methods are implemented in the laboratory setting:
Summary
Although Sorensen titration was the method most widely used for years, the recent use of systems composed of autosamplers and dedicated reagents has made it easier to analyse these compounds at wineries and can replace tedious and imprecise manual protocols with faster, cleaner and more effective methods.
Yeast Assimilable Nitrogen can be measured on the BioSystems Y15, Y200/Y400 and SPICA analysers.
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